OBJECTIVES: 1) To apply 3 bioassays that measure thymic hormone activity to quantitate the inductive activity of thymic and tissue peptides and thymic extracts. These include thymopoietin, FTS, ubiquitin, thymosin and leucotrofina. 2) To apply the same 3 bioassays to test serum from young adult patients with myasthenia gravis and are greater than 3 year after thymectomy. An evaluation will be made to see if clinical benefit from thymectomy equates with significant lowering of thymic hormone activity in one or more bioassays. 3) To see if T cell subpopulations and functions are eventually altered in young adults with greater than 3 years profound thymodeprivation.